Bubble generator

ABSTRACT

A device for the rapid generation of massive quantities of gasfilled, neutrally buoyant bubbles is provided. The device consists of a plurality of parallel struts each streamlined like an airfoil and containing a gas manifold and a bubble film material (BFM) manifold. The generating elements comprise two concentric tubes with the inner tubes connected to the gas manifold and the outer tubes connected to the BFM manifold. The struts are disposed near the discharge end of a cylindrical housing through which an axial air flow is created by a motor and fan plus screens and flow straighteners. The bubbles are pulled off the tips of the outer tubes by the air flow, with the size of the bubbles governed principally by the velocity of the air flow.

United States Patent Ordway et al. [4 1 Nov. 6, 1973 BUBBLE GENERATOR1,676,984 7/1928 Fales CI al 73 147 75 I t D Id nven Ors f gfg ofPrimary Examiner-Herbert Goldlstein NY Attorney-R. S. Sciascia et a1.

[73] Assignee: The United States of America as [57 ABS Q'G LP theSDecetary of the A device for the rapid generation of massive quantitiesas mgton of gas-filled, neutrally buoyant bubbles is provided. [22]Filed: M 30, 1972 The device consists of a plurality of parallel strutseach streamlined like an airfoil and containing a gas manim] APPl-2571787 fold and a bubble film material (EBFM) manifold. The generatingelements comprise two concentric tubes [52] [1.8. CL. 73/147, 46/6 withthe inner tubes nn cted to th gas manifold and 51 161. CI. G01m 9/00 theouter tubes ted to the BFM manifold. The 58 Field 61 Search 46/6, 7, 8;73/147; struts are disposed near the discharge end of a cylindri-239/557; 261/76, 124 cal housing through which an axial air flow iscreated by a motor and fan plus screens and flow straighteners. [56]Refe n Cit d The bubbles are pulled off the tips of the outer tubesUNITED STATES PATENTS by the air flow, with the size of the bubblesgoverned 2 134 890 11/1938 RedOll 73/147 principally by the velocity ofthe 2,616,291 11/1952 Benedum 73/147 2 Claims, 5 Drawing FiguresPATENIEDHuv 6 Ian sum -1 or 2 WISS Fig. I

Fig.5

alvsslass same BF 2 BUBBLE GENERATOR The present invention relates tobubble generating means and, more particularly, to means for generatinggas-filled bubbles at a rate of substantially six million bubbles perminute.

The use of bubbles which conform to or follow the flow of low to mediumvelocity gases is replacing a similar use of smoke primarily because ofthe movement of gases within certain velocity ranges. A hand gun for theproduction of a single stream of bubbles is described in U. S. Pat.application Ser. No. 112,992, filed Feb. 5, 1971, now abandoned,however, it is often desirable to have a massive flow of bubbles, and,obviously, the pistol device in the forementioned application would notserve such a purpose.

The present invention provides a device for generating massivequantities of bubbles which is both desired and necessary in the art ofairflow or fluid flow in applications such as the flow of air pastoutdoor structures or a flow in a very large cross-sectional area wherea multiplicity of bubbles in a single plane at the origin of the bubblesis necessary. The method is accomplished in one embodiment of anapparatus wherein a multiplicity of bubble forming heads are deployedacross the outlet of a large internal diameter bubble generating means.A desired flow rate is produced by an axial fan disposed at the oppositeend of the generating means, and fluctuation damping and flowstraighteners are interposed between the heads and the fan to provide aparallel flow of air. A gas reservoir and a reservoir of bubble filmmaterial are connected by appropriate valves to transverse manifolds,with bubble film material being introduced through one manifold which isconnected to the outer of two co-axial tubes and a gas such as heliumintroduced into the other manifold which is connected to the inner ofthe co-axial tubes.

Accordingly, it is an object of the present invention to provide a novelapparatus for generating massive quantities of gas-filled bubbles.

It is another object of the invention to provide a device for thegeneration of massive quantities of gasfilled bubbles wherein a bubbleflow rate on the order of 6 million bubbles per minute is achieved.

A further object of the invention is to provide a device for generatinga massive quantity of gas-filled bubbles wherein the bubbles areentrained in a parallel flow of air prior to exiting the device.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description thereof whenconsidered in conjunction with the accompanying drawings in which likenumerals represent like parts throughout andwherein:

FIG. 1 is an end view of the bubble generating device.

showing the array of bubble forming orifices and surrounding structuralmembers;

FIG. 2 is a longitudinal section taken along a line sub stantiallyidentical to line 2-2 in FIG. 1;

FIG. 3 is a plan view partly cut away of the discharge end of the deviceshown in FIG. 2;

FIG. 4 is a plan view partly cut away of an individual strut in thedevice; and

FIG. 5 is a sectional view of the strut of FIG. 4 taken along a linesubstantially identical to line 55 in FIG. 4.

Referring to FIGS. 1, 2 and 3, a means for generating an axial flow 11is shown which includes a cylindrical housing 12 having a bellmouthinlet 13 at one end and a plurality of bubble forming heads 15 at theopposite end. The general configuration of housing 12 is cylindrical inthe embodiment shown to enable a substantially straight flow of air tobe produced. It will be appreciated that other configurations thancylindrical may be used to accomplish this result. Disposed in housing12 adjacent bellmouth inlet 13 is an axial flow motor 16 and a fan 17connected thereto, with the motor 16 positioned concentrically withinthe housing by supports 18. Interposed between the head elements 15 andfan 17 are a plurality of means for producing a desirably uniform andstraight flow of air such as a primary screen 21 of selected fine meshin which a high loss of velocity takes place for the advantage ofremoving non-uniformities in the flow of air. After passing throughscreen 21, the air is directed through a flowstraightener 22 which iscomprised of a multiplicity of parallel passages 23 for taking outswirls in the flow of air which may still exist. The air flow is thendirected through a plurality of secondary screens 24 27 which areinserted for the purpose of damping remaining fluctuations andthereafter the straightened flow of air is directed past themultiplicity of head elements 15.

FIG. 1 is an end view of the device showing an array of struts 30, a gasreservoir 31, a valve 32 for controlling the gas admittedinto reservoir31 and a plurality of bubble film material valves 35 for controlling theflow of bubble film material (BFM) in struts 30. FIG.

3 is a plan view of the discharge end of the device partly cutaway toillustrate an individual strut 30 in which the head elements 15 arepositioned.

An individual strut 30 is shown cutaway in FIG. 4 to illustrate themanner in which gas is directed to the head elements via a manifold 36for a lighter-than-air gas such as helium and in which bubble filmmaterial is directed to the head element via a manifold 37. FIG. 5illustrates the exterior shape of the struts 30, having an airfoilcontour at the end 38 which is disposed nearest the secondary screensand nozzle or head end 15 at which bubbles are formed. 1

In operation, a straightened flow of air which is produced by thecombined effect of fan 17, primary screen 21, flow straightener 22 andsecondary screens 24 27, is directed against airfoil section 38 to causea flow of air along the outer surface of nozzle 15 which is nonturbulentand uniform. With gas being introduced through manifold 36 and bubblefilm material being introduced through manifold 37, a bubble necessarilyis formed at the end of nozzle 15 which grows in size as additional gasis forced out from the manifold. Each bubble formed in this manner isswept away from the head element when the drag created by air frictionis sufficient to exert the force necessary to remove the bubble. Bubblesize can be controlled by the velocity of the air flow, with largerbubbles being produced at lower airflow rates and smaller bubbles at ahigher density rate being produced at higher airflow rates. By properadjustment of fan speed and valves 32 and 35, gas-filled bubbles may begenerated continuously and for extremely long periods of time.

In the embodiment shown, which. includes small gage tubing, bubbles offrom about one-sixteenth inch to one-half inch in diameter or somewhatlarger may be generated. For this size bubble, the corresponding massivegenerating rate is about 15,000 bubbles per minute. per liead so thatfor a generator having 20 strutswith 3 20 heads each, or a total of 400heads altogether, a

total generation rate of million bubbles per minutemay be realized.

The bubble generator described herein provides a valuable and uniquetool previously unavailable for the rapid generation of massivequantities of bubbles. A more compact unit of a substantially smallernumber of heads, for example, a semi-portable unit, not shown, havingfrom about to 40 bubble forming elements could be employed invisualizing the complex airflow patterns either about various objects orwithin enclosures. Applications of the smaller unit are to determine airflow in aerodynamic air tunnels, in heating and ventilationinstallation, through blowers and fans, in natural convection studies,in wind flow about buildings, plants etc., in air cooling of electronicsystems, in ground testing of propellers, rotors, and aircraft, and ininternal flow studies such as in pipes, ducts, etc., among other uses.

The unique capabilities of the helium-filled bubbles for visualizationof complex air motions lie in their suitable size and light weight. Thesize described, of about one-sixteenth inch to one-half inch indiameter, allows the motion of individual bubbles to be tracedindependently while their neutral or substantially neutral buoyancyallows them to follow even very low speed flows accurately. Thelifetimes of the bubbles can be adjusted from several seconds up to anindefinite period of time by using various bubble film solutions. Bubblelifetime is controlled primarily by the evaporation rate of the bubblefilm which may be formed from various soap solutions but for superiorcharacteristics the SA] 1035 Bubble Film Solution made by Sage Action,Inc., P. O.

Box 416, Ithaca, N.Y. 14850 may be used. Bubbles from higher qualitysolutions have a longer life, a thinner bubble film and are formed moreeasily than those made by ordinary soap solutions. Films of bubbles madewith the SA] 1035 solution have been demonstrated to possess a minimumlifetime of 30 seconds which is sufficient for most uses. At low speeds,the bubbles appear to be colored and therefore are more visible withrespect to human perception. Bubble streaks are best photographed forpermanent records and for accurate analysis when the shutter speed ofthe camera is slower than the time to generate a single bubble.Consequently, higher generation rates allow faster shutter speeds whichhelp to cut down unfavorable background lighting and overexposure of themodels under study, thereby gaining better contrast for good streakphotographs. The higher quality bubble solution leaves a minimum ofresidue when the film dries and can be made so as not to stain surfacesor clothing.

The bubble motions can be easily photographed by means of conventionalfilm and light sources. With an interrupted light source, the motionappears as broken streaks on the photograph which can be used then toobtain a quantitative measurement of local velocity.

Other means of airflow visualization such as smoke do not possess thesecapabilities since with regards to smoke they are only visible whenthere is a sufficiently high concentration of smoke particles and, inturbulent flows particularly, smoke defuses too rapidly to be of anyvalue. Other means such as balsa dust have larger particles which arealso heavy relative to air and so do not follow rapid fluctuations invelocity or low-speed flows accurately. On the contrary, helium-filledbubbles have been shown to trace airflow patterns at speeds in excess offps. Because of their ability to follow flow steamlines, the bubblesrarely collide with objects in the air stream and are extremely durable.For

example, bubbles have been observed to flow through a fan without impacton the moving blades.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. For example, thebubble generator may be wired for remote operation of the fan, thehelium supply and the bubble film material supply.

What is claimed is:

1. A device for rapidly generating massive quantities of gas-filledneutrally buoyant bubbles for following complex laminar and turbulentairflows comprising:

means for generating a straight, uniform flow of air at controlled flowrates, including flow straightening passages disposed in said deviceand'turbulence removing screens disposed on opposite sides of said flowstraightening passages,

means for forming a multiplicity of streams of neutrally buoyant bubblescontaining a lighter-than-air gas within said flow of air,

said bubble forming means including a plurality of pairs of bubble filmmaterial manifolds and gas manifolds and a conduit connected to each ofsaid manifolds,

said gas manifolds disposed upstream of said bubble film materialmanifolds and the conduits connected to said gas manifolds extendingthrough said bubble film manifolds concentrically into the conduitsconnected thereto and terminating a selected distance from the endsthereof to form bubbles at the ends of said conduits connected to saidbubble film material manifolds,

said bubble film material and gas manifolds arranged parallel to oneanother and said concentric pairs of conduits spaced equally from oneanother to uniformly dispense said bubbles into said airflows.

2. The device as defined in claim 1 wherein said pairs of manifolds aredisposed in struts having an airfoil configuration so as to introduce aminimum of turbulence into said flow of air;

said struts disposed in parallel rows across said generating means sothat said streams of bubbles are dispensed uniformly throughout a crosssection of said flow of air.

l l =8 t i

1. A device for rapidly generating massive quantities of gasfilledneutrally buoyant bubbles for following complex laminar and turbulentairflows comprising: means for generating a straight, uniform flow ofair at controlled flow rates, including flow straightening passagesdisposed in said device and turbulence removing screens disposed onopposite sides of said flow straightening passages, means for forming amultiplicity of streams of neutrally buoyant bubbles containing alighter-than-air gas within said flow of air, said bubble forming meansincluding a plurality of pairs of bubble film material manifolds and gasmanifolds and a conduit connected to each of said manifolds, said gasmanifolds disposed upstream of said bubble film material manifolds andthe conduits connected to said gas manifolds extending through saidbubble film manifolds concentrically into the conduits connected theretoand terminating a selected distance from the ends thereof to formbubbles at the ends of said conduits connected to said bubble filmmaterial manifolds, said bubble film material and gas manifolds arrangedparallel to one another and said concentric pairs of conduits spacedequally from one another to uniformly dispense said bubbles into saidairflows.
 2. The device as defined in claim 1 wherein said pairs ofmanifolds are disposed in struts having an airfoil configuration so asto introduce a minimum of turbulence into said flow of air; said strutsdisposed in parallel rows across said generating means so that saidstreams of bubbles are dispensed uniformly throughout a cross section ofsaid flow of air.